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Not applicable.
The invention refers to a device for applying a coating agent to a cyclically moved substrate, in particular for applying a lubricant to movable sheet metal being supplied to a press in a cycle being adapted to the working cycle of said press.
Presses provided with sheet metal manufacture for performing forming processes like deep-drawing processes, work with a certain working cycle. Therefore, the sheet metal must be supplied to such a press in a synchronized cycle. The advance movement of the sheet metal starts with a phase of acceleration and finishes with a phase of deceleration. Inbetween, there may be a period with constant velocity. Therefore, the advance movement is not constant during a step of advance movement.
With the production of deep-drawing moldings, it is known to coat the sheet metal with a lubricant before the deep-draw process for achieving a high surface quality. Spray valves, e.g. of the kind disclosed in DE 94 08 445 U1 of the applicant have been used hereto up to now. With the known spray valves, the discharge rate of the lubricant is constant during the spray process. Therefore, only with a constant rate of advance a lubricant coating having a constant coating thickness may be achieved. However, during the acceleration and deceleration phases decreasing and increasing coating thicknesses, respectively, are achieved which is undesirable. A too thick layer not only results in an unnecessary consumption of lubricant but may also result in an undesired accumulation of lubricant in the area of the deep-drawing devices.
With the spray valve disclosed in the above indicated DE 94 08 445 U1, the stroke of the nozzle needle and therewith the outlet diameter effected by it may be adjusted. However, the respective adjustment remains constant during a coating process. The adjustability of the outlet diameter here only serves for the adaption to different viscosities of different lubricants which are used for different applications. Thus, the disadvantages of the above indicated kind have to be feared here too.
The problem to be solved by the present invention is to provide a device for the application of a coating agent to a cyclically moved substrate, wherein, with a non-constant advance movement of the substrate, a uniform coating thickness of the coating agent may be achieved.
This problem is solved by the combination of claim 1. Hereby a combination of the above indicated kind is proposed which is provided with at least one spray valve which is permanently supplied with coating agent and at least the nozzle opening of which is adjustable with regard to the size of its effective discharge area in case of change of the rate of advance of the substrate according to the dependency, existing for a constant layer thickness, of the discharge rate of the coating agent out of the spray valve on the rate of advance of the substrate.
The area of the nozzle opening belongs to the parameters influencing the discharge rate of the coating agent out of the spray valve, the discharge rate being most influenced by the change of the area of the nozzle opening. Accordingly, the measures according to the invention advantageously result in a dynamic adaption of the discharge rate to the rate of advance of the substrate. By the amendment of the size of the effective discharge area of the nozzle opening according to the invention, the amount of coating agent supplied to the substrate per time unit may be adjusted continuously in such a way that a constant thickness of the coating agent application is achieved. The discharge rate also depends on other parameters, as already indicated, like the viscosity of the coating agent and the pressure of the coating agent at the spray valve. However, the size of the nozzle opening has the largest influence so that advantageously already small changes are sufficient for achieving an adaption of the discharge rate to a varying rate of advance which is advantageous for avoiding undesired standstill times etc. and allows a simple construction. With the inventive measures, with changing rates of advance of the substrate a constant thickness of the coating agent application is achieved for the first time, and therewith the disadvantages mentioned at the beginning are avoided.
Advantageous embodiment and practical modifications of the generic measures are indicated in the claims. Thus, with the use of spray valves having a valve needle cooperating with an associated seat and being lifted from the seat against the force of a closing spring by means of a control medium and contacting a stop, said stop may practically being formed as a rotatable cam which is at least drivable during changing rates of advance of the substrate and comprises a contour being derived from the dependency, existing for a constant thickness of the coating agent layer, of the discharge rate of the coating agent out of the spray valve on the rate of advance of the substrate. The formation of the stop, associated with the valve needle, as a rotatable cam advantageously enables a very simple and cheap construction of a needle stroke adjustment dynamically adapted to the changing rate of advance and therewith to a discharge rate adapted accordingly. The rotational movement of the cam may simply be achieved and controlled.
If several spray valves arranged side by side in line are necessary, the cams associated with them may advantageously be held on a camshaft traversing above all spray valves, said cam shaft being drivable by means of a drive unit controllable by means of a control device. Hereby it is ensured that only one cam drive unit is necessary for all spray valves of one line.
If several spray valves and spray valve lines, respectively, facing each other are necessary which are associated with drive units, said drive units may be controllable by means of the same control device. By this measure the constructional effort may also be reduced and the accuracy increased.
The control device associated with the cam drive unit is practically formed in such a way that at least for one layer thickness information associated with the connection between rate of advance of the substrate and of the cam may be stored in it. The dependency between the rate of advance and the angle position of the cam may thereby simply be stored in the control device in form of a table. The same applies to the course of the advance movement. This facilitates the data collection and supply.
Further advantageous embodiments and practical modifications of the generic measures are indicated in the remaining claims and may be taken from the following description of examples on the basis of the drawings.